The photocatalytic conditions for decontamination of Kraft effluents from Eucalyptus grandis (Brazil) and Pinus radiata (Chile) were studied. Irradiation in the presence of ZnO was similar for E. grandis and P. radiata effluents reaching a total decolorization after 2 h. This correlates with the mineralization process. When ZnO was immobilized on sand a two-fold faster decolorization was observed after 30 min of irradiation. The combined photochemical-biobleaching process was effective in the decolorization of Eucalyptus Kraft El effluent. By applying a short time of irradiation (10 min) the time necessary for 50% of biological colour reduction was decreased to half. The contribution of the photochemical process when applied as a post-treatment was least evident. In this case additional reduction of about 10% on the AOX content and almost completion of the decolorization process was observed for Pinus Kraft El effluent. Photochemistry applied to pulp and paper industry appeared as an important technique to remediate pollution problems